Where did the slang word "dingleberry" originate?

The exact origin of the slang word ”dingleberry” is not known. The Online Etymology Dictionary suggests that the term is a portmanteau of the words “dangle” and “berry.” This is a likely explanation, as the term can be used to describe a dangling bit of feces.

In modern usage as of 2015, the word dingleberry is a mildly derogatory term most often used to describe an unpopular or despised person. Dingleberry is a synonym for "jerk."

There is scant evidence to support the theory that the word “dingleberry” was coined by an English physicist and contemporary of Albert Einstein named Herbert Dingle, as is the oft-repeated claim of many nonscientific sites on the Internet.